Enhanced quasi-static compressive performance in additively manufactured hierarchically reinforced curved-star lattice metamaterials

Abstract

Auxetic metamaterials, characterized by their negative Poisson’s ratio, offer significant mechanical advantages over conventional cellular structures, rendering them ideal candidates for advanced energy absorption (EA) applications. In this study, a star-shaped configuration was selected as the base geometry, and a progressive design strategy was implemented to enhance its mechanical performance under compressive loading. The novelty of this study lies in converting sharp-cornered star-shaped to curved star-shape (in order to decrease stress concentration) as well as the stepwise hierarchical redesign of the base unit cell through the addition of longitudinal and transverse reinforcing members and the selective removal of shared ligaments. A family of five distinct lattice geometries was designed and fabricated using additive manufacturing. The mechanical behavior of these samples was experimentally evaluated under quasi-static compressive loading using a Santam STM-150 universal testing machine. The analysis was conducted based on nominal stress–strain curves, EA, specific energy absorption (SEA), and the evolution of the Poisson’s ratio as a function of strain. For the specimens examined, the measured SEA values of geometries 2–5 increased by 69.65%, 196.24%, 126.08%, and 102.87%, respectively, compared with the reference curved-star geometry (Geometry 1). Additionally, all modified geometries exhibited higher peak force values than the base geometry. These findings suggest that hierarchical reinforcement, combined with selective line removal, may improve the quasi-static compressive response and EA of the tested curved-star lattices.